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Bigger Coldside?


New member
Sep 27, 2009
Little Rock, AR
the car is an '82 244tic, bone stock as far as engine upgrades goes. I have a BOV installed but not set yet, Sunpro boost gauge, and an MBC -- all the makings for a good time, planning on running 15-18psi once the car is back on the road after some wiring fixes.

I recently purchased a bigger coldside from tryingbe (great guy!) and was wondering how it would flow with the stock .48 A/R hotside on my stock Garrett T3.
The compressor housing I bought is a .52 A/R that has been milled out to fit a compressor wheel from a Buick Grand National. I was told this wheel is the biggest in the T3 "family" and is larger than the Ford Super 60 T3 wheel. I was hoping my Garrett had the .63 A/R hotside that I've heard about but it doesn't. I already pulled the compressor housing and got the turbo off the 85- manifold and started loosening the 6 bolts on the center cartridge to release the coldside.

The dilemma:
I'm afraid the coldside will be too big for the small turbine...I don't know much about how this will impact my flow, but common sense says it won't work well. However, I have been told that the T3 flows surprisingly well...

The question:
Should I just leave the turbo stock and raise the boost or should I go ahead and put the big compressor wheel on and then raise it up? I want the car to be fast, I know that there will be some lag at lower rpm's but I really want to feel it pull once it gets up to 3 or 4 grand. Anybody have any insight on this or maybe they've done something similar?
Should I just be looking for a .63 A/R hotside and bigger turbine wheel?

Once the car is back on the road it's going to have a 90+ manifold and a 3" exhaust. I do have pics of the turbo from stock and the new coldside if anyone wants to see for any reason.

Any help, advice, or insight is MUCH appreciated. My inspection and registration ran out so I need to put this ish back together asap and the turbo is really the biggest thing holding me back right now.

Thanks in advance!!!
i would recommend a better turbine wheel. I had not so good results with what you speak of. too big compressor on an otherwise stock t3.

a better housing too while your at it.

might as well a completely better turbo, haha!
I had that setup a long time ago, it worked out fairly well. you might consider getting a .63 a/r turbine housing, but I'd rock it. What cam are you running?
I had that setup a long time ago, it worked out fairly well. you might consider getting a .63 a/r turbine housing, but I'd rock it. What cam are you running?

.63 A/R turbine housing with what turbine wheel? and I'm running the stock T cam for now but the first day off from work I get after it's on the road I'm running down to a buddy's shop to put my B cam in it. would you recommend selling the B and saving up for an RSI stage 1 or 2?
stage 2 or stage 3. you don't have to put the 63 housing on, but it might be something you consider if the power starts dropping off up top (well, faster than it probably should).
How would you able to add more fuel with k-jet? Bigger turbo flows more air and it needs more fuel.
shouldn't be that bad, the stock .63 wheel/housing isn't that much better imo. it's still a t3/t3, you shouldn't have any problems
How would you able to add more fuel with k-jet? Bigger turbo flows more air and it needs more fuel.

This is true. K-jet is constant injection but it has an air/fuel mixture adjustment on the fuel dizzy. So i can turn up the richness to hit my desired afr once the turbo is on
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I had my fuel distributor shimmed all the way with a 255 in-tank and a .42/.48 @ 20psi and that was all it had. Any bigger of a turbo or more lb/min and I'd run leaner than I would have liked. But, you can get MB gold injectors that flow more and you can get a MB V8 distributor.
A larger comp wheel will lower your turbo speed for a given engine operating point, which when you keep the same turbine wheel, lowers your turbo efficiency. It is possible to make more power since you do have the capability to flow more through the compressor, but it doesn't work as well as increasing the size of both wheels. Since your turbo efficiency is lower at your peak power point, the exhaust backpressure has to be higher for the same boost level, which hurts your power output compared to a correctly size turbine.
from what i've been lead to believe, there's a "window" when matching wheels. my wagon had .63/.42 stock, i put a ford .60 trim t3 compressor on it and it was very well matched imo(which others will agree with - and people have put the the .60 trim on .48 turbines as well). this last time i went too big(t4 60 trim), it didn't look too big, but it is. but it still works just chokes and causes a hilarious comp surge at higher boost levels. but under that level it WORKS JUST FINE. and the "lag" isn't even an issue, i like where the boost comes on, at cruise i'm not running 5psi like others do on a smaller turbo, and if i give it gas it can still build boost and accelerate.

one thing i'm planning on doing since my external manifold is pretty much figured out, gonna try and bypass the small turbine with an external gate. which has been done before with other setups. not ideal, but i have the parts, and it might hold me over till i find a better turbo i can afford
@ around 7:00